Two friends, Joe and Moe, were born in May, one in 1932, the other a year later. Each had an antique grandfather clock of which he was extremely proud. Both of the clocks worked fairly well considering their age, but one clock gained ten seconds per hour while the other one lost ten seconds per hour.

On a day in January, the two friends set both clocks correctly at 12:00 noon.
"Do you realize," asked Joe, "that the next time both of our clocks will show exactly the same time will be on your 47th birthday?"
Moe agreed.